The overall objective of our study is to understand the manner in which the genetic information of mammalian cells is expressed and regulated. Our immediate goal is to describe the steps involved in the synthesis of mRNA in the nucleus and any modification that it may undergo before being expressed in the cytoplasm. Our specific aims are to further purify and characterize individual mouse and rabbit a- and Beta-globin mRNAs, and to define the length of the poly(a) region in each of these messengers. We also hope to define the sequence of events involved with the addition of the poly(A) region and the subsequent loss of this sequence. The characterization of the mRNA in membrane bound polysomes of mouse reticulocytes will also be undertaken. This RNA will be characterized on the basis of its ability to bind to oligo(dt)-cellulose, its ability to direct the synthesis of a- and Beta-chains and the size of its poly(A) region. In order to further characterize the sequence of events from the synthesis of mRNA in the nucleus to its expression in the cytoplasm, the globin mRNA precursor of the nucleus will be isolated.